Pressing ring, joint, and valve

ABSTRACT

A first projection is formed on the outer periphery of a bulb part, a second projection is formed on the socket rear end of the bulb part, a tapered part is formed with a decreasing diameter from the inner periphery of a heel part to the inner periphery of the second projection, and a third projection is formed on the tapered part. A first dimension B from the first projection to the third projection in an inclination direction opposite to an inclination direction G of the tapered part is smaller than a second dimension C from the first projection to the second projection in a radial direction A.

FIELD OF THE INVENTION

The present invention relates to a sealing member used for a joint inwhich a spigot lies in a socket, the joint containing the sealingmember, a pressing ring used for a joint, the joint including thepressing ring, and a valve connected to a pipe via the joint.

BACKGROUND OF THE INVENTION

As shown in FIG. 28, such a conventional sealing member is used for aseparation preventive pipe joint 271 of a slip-on type. In the pipejoint 271, a spigot 275 formed on the end of a pipe 274 lies in a socket273 formed on the end of a pipe 272 connected to the pipe 274.

A sealing member placement recess 276 is formed inside the socket 273and contains a ring-shaped rubber sealing member 277. A lock ring groove278 is formed behind the sealing member placement recess 276. A lockring 279 is attached into the lock ring groove 278. An elastic member280 for centering the lock ring 279 is disposed between the outerperiphery of the lock ring 279 and the bottom of the lock ring groove278. Moreover, a protrusion 281 is formed on the outer periphery of theend of the spigot 275 so as to be engaged with the lock ring 279 fromthe rear of the socket.

As shown in FIGS. 28 and 29, a fitting groove 282 is formed on an innercircumference 284 of the sealing member placement recess 276. Thesealing member 277 includes a heel part 283 that is fit into and engagedwith the fitting groove 282 and a bulb part 285 that is compressedbetween the inner circumference 284 and the outer circumference of thespigot 275 so as to generate a sealing surface pressure.

The bulb part 285 has first to third projections 286 to 288. The firstprojection 286 is formed on the outer circumference of the bulb part 285so as to protrude outward in a radial direction A. The second projection287 is formed on the socket rear end of the bulb part 285.

Moreover, the third projection 288 is formed on the inner circumferenceof the bulb part 285 so as to protrude inward in the radial direction A.The inside diameter of the third projection 288 is set to be smallerthan the outside diameter of the spigot 275. Furthermore, a tapered part289 is formed so as to gradually decrease in diameter from the innercircumference of the heel part 283 to the third projection 288.

With this configuration, as shown in FIG. 28, the heel part 283 is fitinto the fitting groove 282 while the spigot 275 is inserted into thesocket 273. This increases the diameter of the third projection 288 andholds the bulb part 285 between the inner circumference of the socket273 and the outer circumference of the spigot 275. At this point, aclearance between the first projection 286 and the third projection 288is compressed in the radial direction A.

The pipe joint 271 containing the sealing member 277 is described in,for example, Japanese Patent No. 4836870.

Another type of joint is, for example, a pipe joint 301 with a GXspecial pipe connecting cast-iron pipes as shown in FIG. 30. In the pipejoint 301, a spigot 305 formed on the end of a second pipe 304 isinserted into a socket 303 formed on the end of a first pipe 302 to bejoined with the second pipe 304. A peripheral wall 306 radiallyprotruding inward is formed all around the inner circumference of therear part of the socket 303.

Moreover, from an opening end face 307 of the socket 303 to theperipheral wall 306, a sealing member insertion space 308 is formedbetween an outer circumference 305 a of the spigot 305 and an innercircumference 303 a of the socket 303 so as to surround the outercircumference 305 a. An annular sealing member 309 for sealing betweenthe outer circumference 305 a of the spigot 305 and the innercircumference 303 a of the socket 303 lies in the sealing memberinsertion space 308.

Furthermore, a lock ring groove 310 is formed behind the peripheral wall306 so as to surround the spigot 305. The lock ring groove 310 isprovided with a single lock ring 311 having one slit in itscircumference. Moreover, a protrusion 312 is formed around the outercircumference of the end of the spigot 305 so as to be engaged with thelock ring 311 from the rear of the socket.

A pressing ring 313 is fit onto the spigot 305 and is opposed to theopening end face 307 of the socket 303 from the outside. The pressingring 313 presses the sealing member 309 toward the rear of the socket303. The pressing ring 313 is fastened to a flange 316 of the socket 303with a plurality of T-head bolts 314 and nuts 315 and has a pressingface 317 in contact with the end of the sealing member 309 and aprotrusion 318. The protrusion 318 that comes into contact with theopening end face 307 of the socket 303 keeps a distance A from thepressing face 317 to the opening end face 307 of the socket 303 at apredetermined distance.

With this configuration, when the pipes 302 and 304 are joined to eachother, the lock ring 311 is first fit into the lock ring groove 310 andthen the spigot 305 is inserted into the socket 303 until the protrusion112 of the spigot 305 moves on the inner circumference of the lock ring311 to the rear of the socket 303 with the sealing member 309 and thepressing ring 313 fit onto the spigot 305.

Subsequently, the sealing member 309 is inserted into the sealing memberinsertion space 308 from the opening end face 307 of the socket 303, andthen the pressing ring 313 is fastened to the flange 316 of the socket303 with the T-head bolts 314 and the nuts 315. At this point, thefastening of the nuts 315 moves the pressing ring 313 in a pressingdirection B along a tube axis, allowing the pressing face 317 of thepressing ring 313 to press the sealing member 309 in the pressingdirection B so as to press the sealing member 309 into the sealingmember insertion space 308. After that, the protrusion 318 of thepressing ring 313 comes into contact with the opening end face 307 ofthe socket 303, preventing the pressing ring 313 from moving in thepressing direction B. At this point, the fastening of the nuts 315 isstopped to keep the distance A from the pressing face 317 of thepressing ring 313 to the opening end face 107 of the socket 303 at thepredetermined distance. In this case, the rear end of the sealing member309 does not reach the peripheral wall 306, forming a small space 320between the rear end of the sealing member 309 and the peripheral wall306.

When a region where the inner circumference 303 a of the socket 303 andthe outer circumference 305 a of the spigot 305 are opposed in parallelto each other is defined as a compressed region C in the sealing memberinsertion space 308, the sealing member 309 is compressed in a radialdirection D in the compressed region C. This keeps watertightness(sealing property) between the inner circumference 303 a of the socket303 and the outer circumference 305 a of the spigot 305.

The pipe joint 301 including the pressing ring 313 is described in, forexample, Japanese Patent Laid-Open No. 2010-286110.

SUMMARY OF THE INVENTION

In the related art configuration shown in FIGS. 28 and 29, however, whenthe pipes 272 and 274 are joined to each other, the clearance betweenthe first projection 286 and the third projection 288 is compressed inthe radial direction A while a first dimension B from the outercircumference of the first projection 286 to the inner circumference ofthe third projection 288 in the radial direction A is larger than asecond dimension C from the outer circumference of the first projection286 to the inner circumference of the second projection 287 in theradial direction A as shown in FIG. 29. Unfortunately, this increases acompressive force required for compressing the bulb part 285 in theradial direction A. The compressive force increased thus may raise amaximum insertion force required for inserting the spigot 275 into thesocket 273.

In the other related art configuration shown in FIG. 30, a clearance Ebetween the inner circumference 303 a of the socket 303 and the outercircumference 305 a of the spigot 305 is not kept constant but isslightly changed because of the manufacturing tolerances of the socket303 and the spigot 305. Specifically, if the socket 303 has an insidediameter of a maximum manufacturing tolerance while the spigot 305 hasan outside diameter of a minimum manufacturing tolerance, the clearanceE is maximized. Conversely, if the socket 303 has an inside diameter ofa minimum manufacturing tolerance while the spigot 305 has an outsidediameter of a maximum manufacturing tolerance, the clearance E isminimized.

In order to keep sufficient watertightness when the clearance E islarge, the volume of the sealing member 309 needs to be increased toreliably compress the sealing member 309 in the compressed region C.

However, when the volume of the sealing member 309 is increased with thesmall clearance E as shown in FIG. 31, the rear end of the sealingmember 309 reaches the peripheral wall 306 before the protrusion 318 ofthe pressing ring 313 comes into contact with the opening end face 107of the socket 303. This eliminates a space for the sealing member 309 toescape such that the sealing member 309 cannot be pressed into thesealing member insertion space 308 any more.

In this case, an operator cannot visually confirm from the outside thatthe rear end of the sealing member 309 has reached the peripheral wall306. Thus, the operator may forcibly fasten the nuts 315 to bring theprotrusion 318 of the pressing ring 313 into contact with the openingend face 307 of the socket 303. This may apply an extremely large force(excessive force) to the sealing member 309 or the pressing ring 313,failing to join the pipes 302 and 304 to each other.

To address this problem, the compressed region C may be extended to therear of the socket 303 along the tube axis according to an increase inthe volume of the sealing member 309. As the compressed region C isextended, the socket 303 is made longer than that of the related art andthus the spigot 305 needs to be extended accordingly. Unfortunately,this may increase the mass of the pipes 302 and 304.

An object of the present invention is to provide a sealing member and ajoint that can reduce a maximum insertion force required for inserting aspigot into a socket and improve watertightness between the socket andthe spigot. Another object of the present invention is to provide apressing ring, a joint, and a valve that can smoothly join passageforming members such as pipes while bringing the contact part of thepressing ring into contact with the socket, and suppress extension ofthe socket.

In order to attain the objects, a first invention is an annular sealingmember made of an elastic material used for a joint in which a spigotformed on the end of a pipe lies in a socket formed on the end of a pipeto be connected to the other pipe, the sealing member having a heel partfit into a fitting part formed in the socket, and a bulb part disposedbetween the inner circumference of the socket and the outercircumference of the spigot, the bulb part having first to thirdprojections, the first projection being formed on the outer periphery ofthe bulb part so as to protrude outward in a radial direction, thesecond projection being formed on the socket rear end of the bulb part,the bulb part having a tapered part that decreases in diameter from theinner periphery of the heel part to the inner periphery of the secondprojection, the third projection being formed on the tapered part so asto protrude inward in the radial direction, the third projection beingdisposed between the heel part and the second projection in a tube axialdirection, the third projection having an inside diameter smaller thanthe outside diameter of the spigot and larger than the inside diameterof the second projection, the sealing member having a first dimensionfrom the first projection to the third projection in an inclinationdirection opposite to the inclination direction of the tapered part, thefirst dimension being smaller than a second dimension from the outerperiphery of the first projection to the inner periphery of the secondprojection in the radial direction, wherein if the bulb part is heldbetween the inner circumference of the socket and the outercircumference of the spigot lying in the socket, the second projectionincreases in diameter and a portion between the first projection and thethird projection is compressed in the radial direction so as to keepwatertightness between the socket and the spigot.

With this configuration, the heel part of the sealing member is fit intothe fitting part in the socket to insert the spigot into the socket. Atthis point, the end of the spigot comes into contact with the thirdprojection of the sealing member to press the third projection in therearward direction of the socket. This increases the diameter of thesecond projection and draws the third projection in the rearwarddirection of the socket. Thus, a tensile force is generated on the bulbpart in the tube axial direction so as to extend the bulb part in thesocket rearward direction, thereby reducing the first dimension and thecompression margin (compression amount) of the bulb part in the radialdirection.

After that, the end of the spigot compresses the bulb part of thesealing member while passing through the third projection. At thispoint, the portion between the first projection and the third projectionis compressed in the radial direction. In this case, the sealing memberhas the first dimension between the first projection and the thirdprojection such that the first dimension is smaller than the seconddimension from the outer periphery of the first projection to the innerperiphery of the second projection. Thus, the compression margin of thebulb part decreases in the radial direction so as to reduce a maximuminsertion force.

Moreover, between the inner circumference of the socket and the outercircumference of the spigot, the portion between the first projectionand the third projection is compressed in the radial direction so as tokeep watertightness between the socket and the spigot. This can improvethe watertightness between the socket and the spigot.

A sealing member of a second invention has a recess between the heelpart and the first projection and a recess between the heel part and thethird projection.

This configuration reduces a tensile force generated on the bulb partwhen the spigot is inserted into the socket and the third projection ispressed by the end of the spigot in the rearward direction of thesocket, thereby easily increasing the diameter of the second projection.Thus, the protrusion formed on the end of the spigot can easily passthrough the bulb part in the rearward direction of the socket, therebyreducing an insertion force during the joining of the pipes.

A third invention is a joint including the sealing member according tothe first or second invention, wherein the heel part of the sealingmember is fit into the fitting part in the socket, the spigot isinserted into the socket, and the bulb part of the sealing member isdisposed between the inner circumference of the socket and the outercircumference of the spigot.

A fourth invention is a pressing ring in which a spigot formed on asecond passage forming member is inserted into a socket formed on afirst passage forming member to be joined to the second passage formingmember, a peripheral wall protruding inward in a radial direction isformed on the inner periphery of the rear of the socket, and a sealingmember insertion space between an opening end face and a peripheral wallof the socket is formed between the outer circumference of the spigotand the inner circumference of the socket, the pressing ring being usedfor a joint including an annular sealing member lying in the sealingmember insertion space, the pressing ring being opposed to the openingend face of the socket from the outside while being fit onto the spigot,the pressing ring being moved by a pressing member along the axis of thepassage forming member in a pressing direction so as to press thesealing member into the sealing member insertion space, the pressingring having a pressing face that comes into contact with the end of thesealing member, contact portions that come into contact with the socketso as to keep a distance from the pressing face to the opening end faceof the socket at a predetermined distance, and an escaping portion thatallows escape of a part of the sealing member pressed by the pressingface.

With this configuration, when the passage forming members are joined toeach other, the spigot is inserted into the socket with the sealingmember and the pressing ring fit onto the spigot. Subsequently, thesealing member is inserted into the sealing member insertion space fromthe opening end face of the socket, and the pressing ring is moved inthe pressing direction by the pressing member. Thus, the pressing faceof the pressing ring presses the sealing member in the pressingdirection into the sealing member insertion space.

Moreover, the contact portions of the pressing ring are brought intocontact with the socket so as to prevent the pressing ring from movingin the pressing direction. This keeps the distance from the pressingface of the pressing ring to the opening end face of the socket at thepredetermined distance. Thus, the sealing member is compressed in theradial direction in the sealing member insertion space, keepingwatertightness between the inner circumference of the socket and theouter circumference of the spigot.

Furthermore, a clearance between the inner circumference of the socketand the outer circumference of the spigot decreases, and the rear end ofthe sealing member reaches the peripheral wall before the contactportions of the pressing ring come into contact with the socket. Thus,the sealing member cannot be pressed into the sealing member insertionspace any more. Even in this case, the pressing ring is continuouslymoved in the pressing direction by the pressing member, allowing a partof the sealing member pressed by the pressing face of the pressing ringto escape into the escaping portion. This can smoothly bring the contactportions of the pressing ring into contact with the socket. Withoutapplying an extremely large force (excessive force) to the sealingmember and the pressing ring, the passage forming members can besmoothly joined to each other and extension of the socket can besuppressed.

According to the pressing ring of a fifth invention, the escapingportion is a recessed portion that is opened near the opening end faceof the socket opposed to the escaping portion, and the escaping portionis circumferentially formed outside the pressing face in the radialdirection and is recessed from the pressing face in the drawingdirection of the spigot.

With this configuration, even in the case of a small clearance betweenthe inner circumference of the socket and the outer circumference of thespigot, the sealing member pressed by the pressing face of the pressingring partially enters the escaping portion so as to smoothly bring thecontact portions of the pressing ring into contact with the socket.

According to the pressing ring of a sixth invention, the escapingportion has a centering portion that guides the pressing ring in theradial direction so as to align the center of the pressing ring with theaxis of the passage forming member.

With this configuration, when the pressing ring is moved in the pressingdirection by the pressing member, the pressing ring is guided in theradial direction by the centering portion of the escaping portion andthe center of the pressing ring is aligned with the axis of the passageforming member, thereby centering the pressing ring. This does notrequire an operator to lift the pressing ring in the radial directionwhen centering the pressing ring.

According to the pressing ring of a seventh invention, the escapingportion has an inner side-wall face and an outer side-wall face servingas the centering portion, the inner side-wall face and the outerside-wall face are opposed to each other in the radial direction, theouter side-wall face inclines with a decreasing diameter toward the rearof the escaping portion, and the outer side-wall face is in slidingcontact with the end of the sealing member so as to guide the pressingring in the radial direction.

With this configuration, when the pressing ring is moved in the pressingdirection by the pressing member, the outer side-wall face of theescaping portion is in sliding contact with the end of the sealingmember so as to guide the pressing ring in the radial direction,aligning the center of the pressing ring with the axis of the passageforming member.

An eighth invention is a joint including the pressing ring according toany one of the fourth to seventh inventions, wherein the first andsecond passage forming members are pipes, the pressing ring is opposedto the opening end face of the socket from the outside while being fitonto the spigot, and the pressing ring is moved by the pressing memberalong a tube axis in the pressing direction so as to press the sealingmember into the sealing member insertion space until the contactportions come into contact with the socket.

With this configuration, the contact portions of the pressing ring arebrought into contact with the socket so as to smoothly join the pipesand suppress extension of the socket. Accordingly, extension of thespigot and an increase in the mass of the pipe are suppressed.

A ninth invention is a joint including the pressing ring according toany one of the fourth to seventh inventions, wherein one of the firstand second passage forming members is a valve and the other of thepassage forming members is a pipe, the pressing ring is opposed to theopening end face of the socket from the outside while being fit onto thespigot, and the pressing ring is moved by the pressing member along thetube axis in the pressing direction so as to press the sealing memberinto the sealing member insertion space until the contact portions comeinto contact with the socket.

With this configuration, the contact portions of the pressing ring arebrought into contact with the socket so as to smoothly join the valveand the pipe and suppress extension of the socket. Accordingly,extension of the spigot and an increase in the mass of the pipe or thevalve are suppressed.

A tenth invention is a valve connected to a pipe via the joint accordingto the ninth invention, the valve including a valve casing and a valvebody that opens and closes a passage formed in the valve casing, thevalve casing including at least one of the socket and the spigot.

As has been discussed, the present invention can reduce a maximuminsertion force required for inserting a spigot into a socket andimprove watertightness between the socket and the spigot.

Moreover, the present invention can bring the contact portions of apressing ring into contact with the socket so as to smoothly join pipesand suppress extension of the socket. Accordingly, extension of thespigot and an increase in the mass of the pipe or a valve aresuppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the structure of a pipe jointincluding a sealing member according to a first embodiment of thepresent invention.

FIG. 2 shows a cross-sectional structure of the unattached sealingmember alone to be provided in the pipe joint.

FIG. 3 shows cross-sectional views of pipes joined with the pipe joint.

FIG. 4 is a graph showing the relationship between an insertion amountand insertion force of a spigot relative to a socket in the pipe joint.

FIG. 5 is an enlarged cross-sectional view of the compressed anddeformed sealing member with the pipes joined with the pipe joint.

FIG. 6 shows cross-sectional views of the pipes with a minimum clearancebetween the socket and the spigot of the pipe joint.

FIG. 7 shows cross-sectional views of the pipes with a maximum clearancebetween the socket and the spigot of the pipe joint.

FIG. 8 is a partially enlarged cross-sectional view of the pipe jointwith the spigot inclined with respect to the socket by an external forcesuch as an earthquake.

FIG. 9 is a cross-sectional view showing the structure of a joint ofpipes with a pressing ring according to a second embodiment of thepresent invention.

FIG. 10 is a cross-sectional view in which a sealing member is deletedfrom the joint

FIG. 11 is a cross-sectional view of the unattached sealing member aloneto be provided in the joint.

FIG. 12 is a cross-sectional view of the pressing ring of the joint.

FIG. 13 is a cross-sectional view taken along the line X-X of FIG. 12.

FIG. 14 is a cross-sectional view showing a step of mounting thepressing ring of the joint.

FIG. 15 is a cross-sectional view showing a step of mounting thepressing ring of the joint.

FIG. 16 is a cross-sectional view showing a step of mounting thepressing ring of the joint.

FIG. 17 is a cross-sectional view showing a state of the process in themidst of mounting the pressing ring of the joint with a small clearancebetween the socket and the spigot.

FIG. 18 is a cross-sectional view showing a state after the pressingring of the joint is mounted with the small clearance between the socketand the spigot.

FIG. 19 is a front view of a pressing ring according to a thirdembodiment of the present invention.

FIG. 20 is a cross-sectional view taken along the line X-X of FIG. 19.

FIG. 21 is a cross-sectional view taken along the line Y-Y of FIG. 19.

FIG. 22 is a cross-sectional view showing a joint at a point of thepressing face of the pressing ring.

FIG. 23 is a cross-sectional view showing the joint at a point of theescaping portion of the pressing ring.

FIG. 24 is a cross-sectional view showing a state of the process in themidst of mounting the pressing ring with a small clearance between asocket and a spigot.

FIG. 25 is a cross-sectional view showing a state after the pressingring is mounted with the small clearance between the socket and thespigot.

FIG. 26 is a cross-sectional view showing the structure of a joint of apipe and a valve with a pressing ring according to a fourth embodimentof the present invention.

FIG. 27 is a cross-sectional view showing the structure of a joint ofpipes and a valve with a pressing ring according to a fifth embodimentof the present invention.

FIG. 28 is a cross-sectional view showing the structure of a pipe jointincluding a sealing member according to the related art.

FIG. 29 shows a cross-sectional structure of the unattached sealingmember alone to be provided in the pipe joint of FIG. 28.

FIG. 30 is a cross-sectional view showing a pipe joint including apressing ring according to another related art configuration.

FIG. 31 is a cross-sectional view showing the structure of the pipejoint of FIG. 30 with a small clearance between a socket and a spigot.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to the accompanying drawings.

First Embodiment

In a first embodiment, as shown in FIG. 1, reference numeral 1 denotes aseparation preventive pipe joint of a push-on type. A spigot 5 formed onthe end of a pipe 4 lies in a socket 3 formed on the end of another pipe2 connected to the pipe 4.

A sealing member placement recess 6 and a lock ring groove 7 disposedbehind the sealing member placement recess 6 are formed all around theinner circumference of the socket 3. A lock ring 8 having one slit inits circumference is attached to the lock ring groove 7. An elasticbiasing member 9 such as a rubber band for fixing the lock ring 8 isdisposed between the outer circumference of the lock ring 8 and thebottom of the lock ring groove 7. Moreover, a rear end face 11 is formedin a radial direction A in the socket 3 so as to be located between thelock ring groove 7 and the rear of the socket 3. Furthermore, the spigot5 has a protrusion 12 all around the outer circumference of the end ofthe spigot 5 such that the protrusion 12 can be engaged with the lockring 8 from the rear of the socket.

A fitting groove 14 (an example of a fitting part) is formed all aroundthe inner circumference of the sealing member placement recess 6. Aclearance between the socket 3 and the spigot 5 is circumferentiallysealed with an annular sealing member 16 made of rubber (an example ofan elastic material). The sealing member 16 is configured as follows.

FIG. 2 is a cross-sectional view showing the structure of the sealingmember 16 alone that is not attached to the pipe joint 1. The sealingmember 16 has a heel part 17 fit into the fitting groove 14 and a bulbpart 18 held between the inner circumference of the socket 3 (the innercircumference of the sealing member placement recess 6) and the outercircumference of the spigot 5. The heel part 17 is an annular memberthat is rectangular in cross section (perpendicular to a circumferentialdirection in cross section).

The bulb part 18 is an annular member that has first to third bulbs 19to 21 (examples of first to third projections) and first to fourthrecesses 23 to 26. In this configuration, the first bulb 19 has a curvedshape that is formed all around the outer periphery of the bulb part 18so as to protrude outward in the radial direction A.

The second bulb 20 has a curved shape that is formed all around thesocket rear end of the bulb part 18 so as to protrude diagonally to thecenter of the pipe. The bulb part 18 has a tapered part 28 that isformed all around the bulb part 18 so as to gradually decrease indiameter from the inner periphery of the heel part 17 to the innerperiphery of the second bulb 20.

The third bulb 21 has a curved shape that is formed all around thetapered part 28 so as to protrude inward in the radial direction A. Thethird bulb 21 is located between the heel part 17 and the second bulb 20in a tube axial direction D. An inside diameter E1 of the third bulb 21is smaller than an outside diameter E2 of the spigot 5 and is largerthan an inside diameter E3 of the second bulb 20.

A first dimension B from the first bulb 19 to the third bulb 21 in aninclination direction (specifically, a direction that inclines towardthe center of the pipe at the front of the socket 3) opposite to aninclination direction G of the tapered part 28 is smaller than a seconddimension C from the outer periphery of the first bulb 19 to the innerperiphery of the second bulb 20 in the radial direction A.

The first to fourth recesses 23 to 26 all have curved shapes that areformed all around the bulb part 18. In this configuration, the firstrecess 23 is formed between the heel part 17 and the first bulb 19, thesecond recess 24 is formed between the first bulb 19 and the second bulb20, the third recess 25 is formed between the second bulb 20 and thethird bulb 21, and the fourth recess 26 is formed between the third bulb21 and the heel part 17.

The operations of the configuration will be described below.

Referring to FIG. 3, the steps of joining the pipes 2 and 4 will bedescribed below.

(1) The lock ring 8 and the elastic biasing member 9 are fit into thelock ring groove 7, and then the heel part 17 of the sealing member 16is fit into the fitting groove 14 as shown in FIG. 3A, so that the lockring 8, the elastic biasing member 9, and the sealing member 16 areattached into the socket 3.

(2) The spigot 5 is inserted into the socket 3. At this point, as shownin FIG. 3B, the end of the spigot 5 comes into contact with the thirdbulb 21 of the sealing member 16 so as to press the third bulb 21 in arearward direction J of the socket. This increases the diameter of thesecond bulb 20 and draws the third bulb 21 in the rearward direction Jof the socket. Thus, a tensile force is generated on the bulb part 18 inthe tube axial direction D so as to extend the bulb part 18 in thesocket rearward direction J, thereby reducing the first dimension B (SeeFIG. 2) and the compression margin of the bulb part 18 in the radialdirection A.

The formation of the first and fourth recesses 23 and 26 reduces atensile force generated on the bulb part 18 when the end of the spigot 5presses the third bulb 21 in the rearward direction J of the socket,thereby easily increasing the diameter of the second bulb 20. Thus, theprotrusion 12 of the spigot 5 can easily pass through the bulb part 18in the rearward direction J of the socket, thereby reducing an insertionforce during the joining of the pipes.

(3) After that, as shown in FIG. 3C, the protrusion 12 of the spigot 5compresses the bulb part 18 in the radial direction A while passingthrough the inside of the third bulb 21. At this point, the positionalrelationship among the first to third bulbs 19 to 21 is close to atriangle whose apex is the third valve 21 in the socket 3 in the radialdirection A. A clearance between the first bulb 19 and the third bulb 21is compressed in the radial direction A.

In a state in which the sealing member 16 is not compressed or deformedbefore the spigot 5 is inserted into the socket 3, as shown in FIG. 2,the first dimension B is smaller than the second dimension C. Therefore,when the spigot 5 is inserted into the socket 3 to compress and deformthe bulb part 18 of the sealing member 16, the compression margin(compression amount) of the bulb part 18 is reduced.

(4) As shown in FIG. 3D, even after the protrusion 12 of the spigot 5passes through the inside of the third bulb 21, the clearance betweenthe first bulb 19 and the third bulb 21 is compressed in the radialdirection A. Thus, as in the joining step (3), the compression margin ofthe bulb part 18 is reduced so as to reduce a maximum insertion force.

(5) After that, as shown in FIG. 1, the protrusion 12 of the spigot 5passes through the inside of the lock ring 8 to the rear of the socket,thereby joining the pipes 2 and 4.

The pipes 2 and 4 are joined thus. In this state, the clearance betweenthe first bulb 19 and the third bulb 21 is compressed in the radialdirection A between the inner circumference of the socket 3 (the innercircumference of the sealing member placement recess 6) and the outercircumference of the spigot 5 so as to keep watertightness between thesocket 3 and the spigot 5. This can improve the watertightness betweenthe socket 3 and the spigot 5.

As shown in FIG. 1, when a water pressure (fluid pressure) is appliedinto the joined pipes 2 and 4, an extrusion force F1 that extrudes thesealing member 16 from the inside to the outside is applied to thesecond bulb 20. At this point, the third bulb 21 is pressed to the outercircumference of the spigot 5 and thus prevents the extrusion of thesecond bulb 20. When the extrusion of the second bulb 20 is preventedthus, an extrusion force F2 proportionate to the extrusion force F1 isgenerated in the radial direction A on the bulb part 18 by aself-sealing effect, thereby further increasing the watertightness.

FIG. 4 is a graph showing the relationship between an insertion amountand an insertion force of the spigot 5 relative to the socket 3. In FIG.4, a graph M1 indicated by a solid line corresponds to the firstembodiment and has two peaks P1 and P2 having a maximum insertion force.The first insertion force peak P1 appears when the bulb part 18 isextended in the rearward direction J of the socket by pressing the thirdbulb 21 with the end of the spigot 5 in the rearward direction J of thesocket in the joining step (2) of FIG. 3B. After that, the secondinsertion force peak P2 appears when the bulb part 18 is compressed inthe radial direction A by passing the protrusion 12 of the spigot 5through the inside of the third bulb 21 in the joining step (3) of FIG.3C.

In the first embodiment, when the spigot 5 is inserted into the socket3, the bulb part 18 is extended mainly in the rearward direction J ofthe socket and the bulb part 18 is compressed mainly in the radialdirection A at different times according to the insertion amount of thespigot 5. The insertion force of the spigot 5 to the socket 3 is thusdispersed to the two peaks P1 and P2, thereby decreased.

In contrast, a second graph M2 indicated by a dotted line corresponds tothe related art shown in FIGS. 28 and 29 with a single peak P. Accordingto the related art, when the spigot 275 is inserted into the socket 273,the bulb part 285 is extended mainly in the rearward direction of thesocket and the bulb part 285 is compressed mainly in the radialdirection A substantially at the same time according to the insertionamount of the spigot 275. Thus, the insertion force of the spigot 5 tothe socket 3 is not dispersed but is concentrated on the peak P, therebyincreased.

In the explanation, as shown in FIG. 5, a clearance S between the innerperiphery of the socket 3 and the outer periphery of the spigot 5 is astandard clearance (that is, the clearance S has a specified dimension).In this case, the position of the third bulb 21 is hardly displaced fromthe position of the first bulb 19 in an insertion direction H, resultingin only a small displacement 30 between the position of the first bulb19 and the position of the third bulb 21 in the tube axial direction D.

In contrast, if the socket 3 has an inside diameter of a minimummanufacturing tolerance and the spigot 5 has an outside diameter of amaximum manufacturing tolerance, as shown in FIG. 6, the clearance S isminimized. In the case of the minimum clearance S, an engagement margin(engagement amount) between the third bulb 21 and the end of the spigot5 increases. Thus, as compared with the case of the standard clearance Sshown in FIGS. 3 and 5, the third bulb 21 is further drawn into the rearpart of the socket 3. This further reduces the first dimension B (SeeFIG. 2) compared to that of the standard clearance S, causing the bulbpart 18 to have a smaller compression margin in the radial direction A.

When the pipes 2 and 4 are joined, the clearance between the first bulb19 and the third bulb 21 is compressed in the radial direction A,thereby reducing the compression margin of the bulb part 18 and themaximum insertion force.

As shown in FIG. 6B, in the case of the minimum clearance S, the thirdbulb 21 is further drawn into the rear part of the socket 3. Thisdisplaces the position of the third bulb 21 from the position of thefirst bulb 19 in the insertion direction H, causing the displacement 30between the position of the first bulb 19 and the position of the thirdbulb 21 in the tube axial direction D to be larger than the displacement30 of the standard clearance S. In this case, the compression margin ofthe bulb part 18 in the radial direction A decreases and thus theinsertion force of the spigot 5 with the minimum clearance S isconsiderably smaller than in the related art shown in FIGS. 28 and 29.

If the socket 3 has an inside diameter of the maximum manufacturingtolerance while the spigot 5 has an outside diameter of the minimummanufacturing tolerance, as shown in FIG. 7, the clearance S ismaximized. In the case of the maximum clearance S, the diameter of thesecond bulb 20 is increased by the spigot 5 when the pipes 2 and 4 arejoined. At this point, an increase in the diameter of the second bulb 20is smaller than that of the standard clearance S. As shown in FIG. 7B,the first bulb 19 comes into contact with the inner circumference of thesocket 3 while the second bulb 20 and the third bulb 21 come intocontact with the outer circumference of the spigot 5. In this state, aportion between the first bulb 19 and the second and third bulbs 20 and21 is compressed in the radial direction A, thereby obtainingwatertightness between the socket 3 and the spigot 5.

Moreover, an external force applied to the pipe joint 1 and the pipes 2and 4 by an earthquake or the like may bend the pipe joint 1 or flattenthe pipes 2 and 4. For example, as shown in FIG. 8, even if the spigot 5is inclined with respect to the socket 3, the first bulb 19 comes intocontact with the inner circumference of the socket 3 and the third bulb21 comes into contact with the outer circumference of the spigot 5. Inthis state, a water pressure applied into the pipes 2 and 4 causes theextrusion force F1 to be applied to the second bulb 20 so as to deformthe bulb part 18. Furthermore, the extrusion force F2 proportionate tothe extrusion force F1 is generated in the radial direction A on thebulb part 18 by the self-sealing effect, thereby further increasing thewatertightness.

As shown in FIG. 8, even if the spigot 5 is inclined with respect to thesocket 3 such that the clearance S between the inner periphery of thesocket 3 and the outer periphery of the spigot 5 increases from the rearof the socket 3 toward the opening end of the socket 3, the third bulb21 is reliably pressed to the outer circumference of the spigot 5 by theinward extrusion force F2 in the radial direction, thereby preventinginsufficient provision of watertightness between the third bulb 21 andthe outer circumference of the spigot 5.

Typically, as the pipes 2 and 4 increase in diameter, the spigot 5decreases in stiffness, facilitating flattening of the pipes 2 and 4.Thus, even if the pipes 2 and 4 having large diameters are flattened byan external force other than earthquakes, the extrusion force F2proportionate to the extrusion force F1 is generated in the radialdirection A of the bulb part 18 by the self-seal effect as in the caseof the earthquake, thereby improving the watertightness.

Second Embodiment

As shown in FIGS. 9 and 10, a joint 122 in a second embodiment is a pipejoint that joins a first pipe 102 (an example of a first passage formingmember) and a second pipe 104 (an example of a second passage formingmember). In the joint 122, a spigot 105 formed on the end of the secondpipe 104 lies in a socket 103 formed on the end of the first pipe 102 tobe joined to the second pipe 104. A peripheral wall 106 protrudinginward in a radial direction is formed all around the innercircumference of the rear of the socket 103.

Moreover, between an opening end face 107 and the peripheral wall 106 ofthe socket 103, a sealing member insertion space 108 is formed betweenan outer circumference 105 a of the spigot 105 and an innercircumference 103 a of the socket 103 so as to surround the spigot 105.An annular sealing member 123 lies in the sealing member insertion space108 so as to seal a space between the outer circumference 105 a of thespigot 105 and the inner circumference 103 a of the socket 103.

In the sealing member insertion space 108, a region where the innercircumference 103 a of the socket 103 and the outer circumference 105 aof the spigot 105 are opposed in parallel to each other is defined as acompressed region C. The inner circumference 103 a of the socket 103 hasa tapered part 103 b between the opening end face 107 and the compressedregion C. The tapered part 103 b increases in diameter from the rear ofthe socket 103 to the opening end face 107.

Furthermore, behind the peripheral wall 106, a lock ring groove 110 isformed all around the inner circumference of the socket 103. A lock ring111 having one slit in its circumference is attached to the lock ringgroove 110. Furthermore, the spigot 105 has a protrusion 112 around theouter circumference of the end of the spigot 105 such that theprotrusion 112 can be engaged with the lock ring 111 from the rear ofthe socket.

A pressing ring 131 that presses the sealing member 123 to the rear ofthe socket 103 is fit onto the spigot 105 and is opposed to the openingend face 107 of the socket 103 from the outside.

As shown in FIG. 11, the sealing member 123 is an annular member made ofan elastic material such as rubber. The sealing member 123 in crosssection is a combination of a circular end 123 a that is circularlyformed at the insertion end of the sealing member 123 and a trapezoidalbase portion 123 b that decreases in thickness toward the circular end123 a and increases in thickness toward the pressing ring 131.

As shown in FIGS. 9, 12, and 13, the pressing ring 131 is fastened to aflange 116 of the socket 103 with a plurality of T-head bolts 114 (anexample of a pressing member) and nuts 115 (an example of a pressingmember) so as to move along a tube axis 119 (See FIG. 16) in a pressingdirection B.

The pressing ring 131 has a central opening 132 where the spigot 105 isinserted, a plurality of bolt insertion holes 133, a pressing-ring endface 134 opposed to the opening end face 107 of the socket 103, apressing face 135 that comes into contact with the end face of the baseportion 123 b of the sealing member 123 so as to press the sealingmember 123, a plurality of protrusions 136 (an example of a contactportion) that come into contact with the opening end face 107 of thesocket 103 so as to keep a distance A (See FIG. 10) from the pressingface 135 to the opening end face 107 of the socket 103 at apredetermined distance, and an escaping portion 137 that allows escapeof the base portion 123 b of the sealing member 123 pressed by thepressing face 135.

The protrusions 136 are formed outside of the bolt insertion holes 133in a radial direction D. The pressing face 135 is located inside of thepressing-ring end face 134 in a drawing direction F of the spigot 105and is formed all within the inner periphery of the pressing-ring endface 134. This configuration forms a step in a tube axial directionbetween the pressing face 135 and the pressing-ring end face 134.

The escaping portion 137 is a recessed portion (grooved portion) that isopened near the opening end face 107 of the socket 103 opposed to theescaping portion 137. The escaping portion 137 is circumferentiallyformed so as to be located outside of the pressing face 135 in theradial direction D and between the pressing face 135 and thepressing-ring end face 134 in the radial direction D. The escapingportion 137 is recessed from the pressing face 135 in the drawingdirection F of the spigot 105.

The escaping portion 137 has an inner side-wall face 137 a, an outerside-wall face 137 b, and a rear face 137 c. The inner side-wall face137 a and the outer side-wall face 137 b are opposed to each other inthe radial direction D, and the rear face 137 c is formed between therear end of the inner side-wall face 137 a and the rear end of the outerside-wall face 137 b. The outer side-wall face 137 b is an example of acentering portion that guides the pressing ring 131 in the radialdirection D so as to align the center of the pressing ring 131 with thetube axis 119 (See FIG. 16, an example of the axis of the passageforming member). The outer side-wall face 137 b decreases in diametertoward the rear of the escaping portion 137.

A width G of the pressing face 135 in the radial direction D in FIG. 12is set at about 30% to 70% of a width H of the base portion 123 b of thesealing member 123 in FIG. 11. The width G of the pressing face 135 isexpressed by the following equation: the width G=(the outside diameterof the pressing face 135−the inside diameter of the pressing face135)/2. The width H of the base portion 123 b of the sealing member 123is expressed by the following equation: the width H=(the outsidediameter of the base portion 123 b−the inside diameter of the baseportion 123 b)/2.

The operations of the configuration will be described below.

When the pipes 102 and 104 are joined, as shown in FIG. 14, the lockring 111 is first fit into the lock ring groove 110 in the socket 103,and then the sealing member 123 and the pressing ring 131 are fit ontothe spigot 105. In this state, the spigot 105 is inserted into thesocket 103 until the protrusion 112 of the spigot 105 inside the lockring 111 reaches the rear of the socket 103.

After that, the circular end 123 a of the sealing member 123 is broughtinto contact with the tapered part 103 b of the socket 103, and then theT-head bolts 114 are inserted into bolt through holes 124 of the flange116 of the socket 103 and the bolt insertion holes 133 of the pressingring 131. At this point, the pressing ring 131 is moved down by the selfweight and thus the center of the pressing ring 131 is located under thetube axis 119. A clearance between the inner periphery of the pressingring 131 and the outer periphery of the spigot 105 in the radialdirection D is minimized (=0) at the upper end and is maximized at thelower end.

After that, as shown in FIG. 15, the nuts 115 are screwed onto theT-head bolts 114 so as to move the pressing ring 131 in the pressingdirection B. Thus, the pressing face 135 of the pressing ring 131 comesinto contact with the end face of the base portion 123 b of the sealingmember 123 so as to press the sealing member 123 in the pressingdirection B. This presses the sealing member 123 into the sealing memberinsertion space 108. At this point, the outer side-wall face 137 b ofthe escaping portion 137 is in sliding contact with an outer end corner123 c of the base portion 123 b of the sealing member 123. Thus, thepressing ring 131 is guided in the radial direction D so as to climb upwith respect to the spigot 105. This moves the center of the pressingring 131 upward to the tube axis 119 so as to automatically center thepressing ring 131. Hence, an operator does not need to lift the pressingring 131 in the radial direction D when centering the pressing ring 131.

Subsequently, as shown in FIG. 16, the protrusions 136 of the pressingring 131 come into contact with the opening end face 107 of the socket103 so as to prevent the pressing ring 131 from moving in the pressingdirection B. The fastening of the nuts 115 is stopped at this point soas to keep the distance A from the pressing face 135 of the pressingring 131 to the opening end face 107 of the socket 103 at thepredetermined distance. At this point, the rear end of the sealingmember 123 does not reach the peripheral wall 106, forming a small space120 between the rear end of the sealing member 123 and the peripheralwall 106.

As shown in FIG. 9, the circular end 123 a of the sealing member 123 iscompressed in the radial direction D in the compressed region C, therebykeeping watertightness between the inner circumference 103 a of thesocket 103 and the outer circumference 105 a of the spigot 105.

The joint 122 shown in FIGS. 9 and 16 has a sufficient clearance Ebetween the inner circumference 103 a of the socket 103 and the outercircumference 105 a of the spigot 105. As shown in FIG. 17, if amanufacturing tolerance reduces the clearance E, the rear end of thesealing member 123 reaches the peripheral wall 106 before theprotrusions 136 of the pressing ring 131 come into contact with theopening end face 107 of the socket 103. Thus, the sealing member 123 maynot be pressed into the sealing member insertion space 108 any more.Even in this case, the nuts 115 are further fastened to move thepressing ring 131 in the pressing direction B, allowing the end of thebase portion 123 b of the sealing member 123 pressed by the pressingface 135 of the pressing ring 131 to enter the escaping portion 137 asshown in FIG. 18.

The sealing member 123 that cannot be pressed any more finally escapesinto the escaping portion 137, smoothly bringing the protrusions 136 ofthe pressing ring 131 into contact with the opening end face 107 of thesocket 103. This can smoothly join the pipes 102 and 104 and suppressextension of the socket 103 without applying an extremely large force(excessive force) to the sealing member 123 and the pressing ring 131.Thus, an increase in cost can be suppressed.

As indicated by a dotted part of FIG. 10, if a predetermined gap region140 surrounded by the pressing face 135, the escaping portion 137 of thepressing ring 131, the inner circumference 103 a of the socket 103, theouter circumference 105 a of the spigot 105, and the peripheral wall 106has a volume V1 while the sealing member 123 has a volume V2, the sizeof the escaping portion 137 is set such that the volume V1 of thepredetermined gap region 140 is not smaller than the volume V2 of thesealing member 123 (that is, V1≥V2).

The volume V1 is determined by multiplying the cross-sectional area ofthe gap region 140 by the circumference of the centroid of the gapregion 140. The volume V2 is determined by multiplying thecross-sectional area of the sealing member 123 by the circumference ofthe centroid of the sealing member 123.

Moreover, the width G (See FIG. 12) of the pressing face 135 is set atabout 30% to 70% of the width H (See FIG. 11) of the base portion 123 bof the sealing member 123. If the width G is set smaller than about 30%of the width H, the end face of the base portion 123 b of the sealingmember 123 may receive an extremely small force from the pressing face135 of the pressing ring 131. Thus, the pressing face 135 may press thesealing member 123 with an insufficient force in the pressing directionB.

If the width G is set larger than about 70% of the width H, the outsidediameter of the pressing face 135 of the pressing ring 131 increases,the outside diameter of the escaping portion 137 remains constant, andthe inside diameter of the escaping portion 137 increases. This reducesthe volume (internal capacity) of the escaping portion 137. In the caseof the small clearance E, the sealing member 123 may insufficientlyescape into the escaping portion 137, leading to difficulty in bringingthe protrusions 136 of the pressing ring 131 into contact with theopening end face 107 of the socket 103.

Third Embodiment

In the second embodiment, as shown in FIG. 13, the pressing face 135 andthe escaping portion 137 are formed all around the pressing ring 131. Inthe following third embodiment, as shown in FIGS. 19 to 21, pressingfaces 135 and escaping portions 137 are divided into sections in thecircumferential direction of a pressing ring 131.

Specifically, the pressing faces 135 are formed at four locations spaced90° apart in the circumferential direction of the pressing ring 131, thepressing face 135 having a predetermined angle α. The escaping portions137 are formed between the pressing faces 135 in the circumferentialdirection of the pressing ring 131, the escaping portion 137 having apredetermined angle β. As shown in FIG. 21, the escaping portion 137 hasan outer side-wall face 137 b and a rear face 137 c. The inner peripheryof the escaping portion 137 communicates with a central opening 132 ofthe pressing ring 131. As in the second embodiment, the outer side-wallface 137 b is an example of a centering portion that guides the pressingring 131 in a radial direction D and inclines to decrease in diametertoward the rear of the escaping portion 137.

The operations of the configuration will be described below.

As shown in FIGS. 22 and 23, protrusions 136 of the pressing ring 131come into contact with an opening end face 107 of a socket 103 so as toprevent the pressing ring 131 from moving in a pressing direction B. Thefastening of nuts 115 is stopped at this point so as to keep a distanceA from the pressing face 135 of the pressing ring 131 to the opening endface 107 of the socket 103 at a predetermined distance. At this point,the rear end of a sealing member 123 does not reach a peripheral wall106, forming a small space 120 between the rear end of the sealingmember 123 and the peripheral wall 106.

A joint 122 shown in FIGS. 22 and 23 has a sufficiently large clearanceE between an inner circumference 103 a of the socket 103 and an outercircumference 105 a of a spigot 105. As shown in FIG. 24, in contrast,if a manufacturing tolerance reduces the clearance E, the rear end ofthe sealing member 123 reaches the peripheral wall 106 before theprotrusions 136 of the pressing ring 131 come into contact with theopening end face 107 of the socket 103. Thus, the sealing member 123 maynot be pressed into a sealing member insertion space 108 any more. Evenin this case, the nuts 115 are further fastened to move the pressingring 131 in the pressing direction B, allowing the end of a base portion123 b of the sealing member 123 to enter the escaping portion 137 asshown in FIG. 25.

The sealing member 123 that cannot be pressed any more finally escapesinto the escaping portion 137 so as to smoothly bring the protrusions136 of the pressing ring 131 into contact with the opening end face 107of the socket 103. This can smoothly join pipes 102 and 104 and suppressextension of the socket 103 without applying an extremely large force(excessive force) to the sealing member 123 and the pressing ring 131.Thus, an increase in cost can be suppressed.

As in the second embodiment, when the pipes 102 and 104 are joined toeach other, the outer side-wall face 137 b of the escaping portion 137is in sliding contact with an outer end corner 123 c of the base portion123 b of the sealing member 123. Thus, the pressing ring 131 is guidedin the radial direction D so as to be automatically centered. This doesnot require an operator to lift the pressing ring 131 in the radialdirection D when centering the pressing ring 131.

In the third embodiment, as shown in FIG. 19, the pressing ring 131 hasthe four pressing faces 135 and the four escaping portions 137. Thenumber of locations is not limited to four.

In the second and third embodiments, as shown in FIGS. 9 and 22, thefirst pipe 102 was described as an example of a first passage formingmember, the second pipe 104 was described as an example of a secondpassage forming member, and a pipe joint was described as the joint 122.The joint 122 is not limited to a joint for the pipes 102 and 104. Forexample, as will be described in a fourth embodiment that will bedescribed below, a joint may be provided to join a valve and a pipe.

Fourth Embodiment

As shown in FIG. 26, a joint 150 in a fourth embodiment joins asoft-seal gate valve 151 (an example of a first passage forming member)and a pipe 152 (an example of a second passage forming member). Thesoft-seal gate valve 151 includes a valve casing 153 and a valve body155 that opens and closes a passage 154 formed in the valve casing 153.

The valve casing 153 has a pair of sockets 103 that serve as the inletand outlet of a fluid. A spigot 105 is provided on one end of the pipe152. The spigot 105 lying in the socket 103 constitutes the joint 150including the gate valve 151 and the pipe 152. The structure of thejoint 150 is identical to that of the joint 122 according to the secondor third embodiment, and thus the detailed explanation thereof isomitted.

With this configuration, the same operations and effect can be obtainedas in the second or third embodiment. Protrusions 136 of a pressing ring131 are brought into contact with an opening end face 107 of the socket103 so as to smoothly join the gate valve 151 and the pipe 152 andsuppress extension of the socket 103. Thus, an increase in cost can besuppressed.

In the fourth embodiment, as shown in FIG. 26, the gate valve 151 wasdescribed as an example of the first passage forming member. Other kindsof valves other than the gate valve are also applicable.

In the fourth embodiment, as shown in FIG. 26, the gate valve 151 wasdescribed as an example of the first passage forming member and the pipe152 was described as an example of the second passage forming member.The pipe 152 may be an example of the first passage forming member andthe gate valve 151 may be an example of the second passage formingmember. In this case, the socket 103 is provided on the one end of thepipe 152 and a pair of spigots 105 is provided on the valve casing 153of the gate valve 151.

Fifth Embodiment

In the fourth embodiment, as shown in FIG. 26, the valve casing 153includes the pair of sockets 103. In a fifth embodiment that will bedescribed below, as shown in FIG. 27, a valve casing 153 may have asocket 103 and a spigot 105. In this case, the spigot 105 of a pipe 152is inserted into the socket 103 of a gate valve 151 so as to constitutea joint 150 while the spigot 105 of the gate valve 151 is inserted intothe socket 103 of another pipe 156 so as to constitute a joint 150.

With this configuration, the same operations and effect can be obtainedas in the fourth embodiment.

In the second to fifth embodiments, as shown in FIGS. 9, 22, 26, and 27,the pressing ring 131 includes the protrusions 136, an example of acontact portion. The protrusions may be provided on the opening end face107 of the socket 103, and the pressing ring 131 may have contactportions on the protrusions of the socket 103.

Having described the invention, the following is claimed:
 1. A pressingring for pressing an annular sealing member of a joint to a rear of asocket of the joint, wherein the socket is formed on a first passageforming member, wherein the spigot is formed on a second passage formingmember and lies in the socket, wherein the annular sealing member liesin a sealing member insertion space, wherein an inner periphery of therear of the socket has a peripheral wall protruding inward in a radialdirection of the second passage forming member, wherein the sealingmember insertion space is located between an opening end face of thesocket, the peripheral wall of the socket, an outer circumference of thespigot, and an inner circumference of the socket, wherein the pressingring is fitted onto the spigot, wherein the joint joins the firstpassage forming member and the second passage forming member, whereinthe spigot lies in the socket, wherein the pressing ring is movable by apressing member along an axis of the second passage forming member in apressing direction, wherein the pressing ring is fastened to the socketwith a plurality of bolts, the pressing ring comprising: a plurality ofbolt insertion holes into which the plurality of bolts are inserted; apressing face in contact with an end of the annular sealing member andarranged opposing the opening end face of the socket at a predetermineddistance from the opening end face of the socket, the pressing facebeing configured to press the annular sealing member; a plurality ofprotrusions arranged outside of the plurality of bolt insertion holes inthe radial direction of the second passage forming member to contact theopening end face of the socket and arrange the pressing face at thepredetermined distance from the opening end face of the socket; and anescaping portion dimensioned to allow a part of the annular sealingmember to escape when the part of the annular sealing member is pressedby the pressing face, the escaping portion being a recessed portiondimensioned to create an opening near an area of the opening end face ofthe socket that is opposed to the escaping portion, the escaping portionbeing arranged inside of the plurality of bolt insertion holes in theradial direction of the second passage forming member and outside of thepressing face in the radial direction of the second passage formingmember, the escaping portion being recessed from the pressing face in adrawing direction of the spigot, wherein, in the radial direction of thesecond passage forming member, a clearance between the innercircumference of the socket and the outer circumference of the spigot isless than a distance between the outer circumference of the spigot andthe escaping portion.
 2. The pressing ring according to claim 1, whereinthe protrusions are arranged adjacent to an outer circumference of thepressing ring.
 3. The pressing ring according to claim 1, wherein theprotrusions project in the pressing direction.
 4. The pressing ringaccording to claim 1, wherein positions at which the protrusions arearranged respectively correspond with positions at which the pluralityof bolt insertion holes is formed.
 5. The pressing ring according toclaim 1, wherein the protrusions are arranged in line with the pluralityof bolt insertion holes in the radial direction of the second passageforming member.
 6. The pressing ring according to claim 1, wherein theperipheral wall of the inner periphery of the rear of the socketprotrudes inward from the inner circumference of the socket, wherein thesealing member insertion space is formed between the opening end face ofthe socket and the peripheral wall of the socket along a shared axis ofthe first and second passage forming members, wherein the end of theannular sealing member that is in contact with the pressing face is afront end of the annular sealing member, wherein the part of the annularsealing member that escapes into the escaping portion is the front endof the annular sealing member, wherein the pressing face is configuredto press the front end of the annular sealing member such that a rearend of the annular sealing member contacts the peripheral wall of thesocket before the plurality of protrusions contact the opening end faceof the socket, and wherein the rear end of the annular sealing memberthat is in contact with the peripheral wall of the socket is inhibitedby the peripheral wall of the socket from moving further into thesealing member insertion space.
 7. The pressing ring according to claim1, wherein the escaping portion has a centering portion that guides thepressing ring in the radial direction so as to align a center of thepressing ring with the axis of the second passage forming member.
 8. Thepressing ring according to claim 7, wherein the escaping portion has aninner side-wall face and an outer side-wall face serving as thecentering portion, wherein the inner side-wall face and the outerside-wall face are opposed to each other in the radial direction of thesecond passage forming member, wherein the outer side-wall face isinclined with a decreasing diameter toward a rear of the escapingportion, and wherein the outer side-wall face is in sliding contact withthe end of the annular sealing member so as to guide the pressing ringin the radial direction of the second passage forming member.
 9. A jointfor joining a first passage forming member and a second passage formingmember, the joint comprising: a socket formed on the first passageforming member, a rear of the socket having an inner periphery, theinner periphery having a peripheral wall protruding inward in a radialdirection of the second passage forming member; a spigot formed on thesecond passage forming member, the spigot lying in the socket; anannular sealing member positioned within a sealing member insertionspace, the sealing member insertion space being located between anopening end face of the socket, the peripheral wall of the socket, anouter circumference of the spigot, and an inner circumference of thesocket; a plurality of bolts; and a pressing ring fastened to the socketwith the plurality of bolts and fitted onto the spigot, the pressingring being configured to press the annular sealing member to the rear ofthe socket, the pressing ring being movable by a pressing member alongan axis of the second passage forming member in a pressing direction,the pressing ring comprising: a plurality of bolt insertion holes intowhich the plurality of bolts are inserted; a pressing face in contactwith an end of the annular sealing member and arranged opposing theopening end face of the socket at a predetermined distance from theopening end face of the socket, the pressing face being configured topress the annular sealing member; a plurality of protrusions arrangedoutside of the plurality of bolt insertion holes in the radial directionof the second passage forming member to contact the opening end face ofthe socket and arrange the pressing face at the predetermined distancefrom the opening end face of the socket; and an escaping portiondimensioned to allow a part of the annular sealing member to escape whenthe part of the annular sealing member is pressed by the pressing face,the escaping portion being a recessed portion dimensioned to create anopening near an area of the opening end face of the socket that isopposed to the escaping portion, the escaping portion being arrangedinside of the plurality of bolt insertion holes in the radial directionof the second passage forming member and outside of the pressing face inthe radial direction of the second passage forming member, the escapingportion being recessed from the pressing face in a drawing direction ofthe spigot, wherein, in the radial direction of the second passageforming member, a clearance between the inner circumference of thesocket and the outer circumference of the spigot is less than a distancebetween the outer circumference of the spigot and the escaping portion,wherein the first and second passage forming members are pipes, andwherein the pressing ring is movable by the pressing member along theaxis of the second passage forming member in the pressing direction soas to press the annular sealing member into the sealing member insertionspace until the protrusions contact the socket.
 10. The joint accordingto claim 9, wherein the protrusions are arranged adjacent to an outercircumference of the pressing ring.
 11. The joint according to claim 9,wherein the protrusions project in the pressing direction.
 12. The jointaccording to claim 9, wherein positions at which the protrusions arearranged respectively correspond with positions at which the pluralityof bolt insertion holes is formed.
 13. The joint according to claim 9,wherein the protrusions are arranged in line with the plurality of boltinsertion holes in the radial direction of the second passage formingmember.
 14. The joint according to claim 9, wherein the peripheral wallof the inner periphery of the rear of the socket protrudes inward fromthe inner circumference of the socket, wherein the sealing memberinsertion space is formed between the opening end face of the socket andthe peripheral wall of the socket along a shared axis of the first andsecond passage forming members, wherein the end of the annular sealingmember that is in contact with the pressing face is a front end of theannular sealing member, wherein the part of the annular sealing memberthat escapes into the escaping portion is the front end of the annularsealing member, wherein the pressing face is configured to press thefront end of the annular sealing member such that a rear end of theannular sealing member contacts the peripheral wall of the socket beforethe plurality of protrusions contact the opening end face of the socket,and wherein the rear end of the annular sealing member that is incontact with the peripheral wall of the socket is inhibited by theperipheral wall of the socket from moving further into the sealingmember insertion space.
 15. A joint for joining a first passage formingmember and a second passage forming member, the joint comprising: asocket formed on the first passage forming member, a rear of the sockethaving an inner periphery, the inner periphery having a peripheral wallprotruding inward in a radial direction of the second passage formingmember; a spigot formed on the second passage forming member, the spigotlying in the socket; an annular sealing member positioned within asealing member insertion space, the sealing member insertion space beinglocated between an opening end face of the socket, the peripheral wallof the socket, an outer circumference of the spigot, and an innercircumference of the socket; a plurality of bolts; and a pressing ringfitted onto the spigot, the pressing ring being configured to press theannular sealing member to the rear of the socket, the pressing ringbeing movable by a pressing member along an axis of the second passageforming member in a pressing direction, the pressing ring comprising: aplurality of bolt insertion holes into which the plurality of bolts areinserted; a pressing face in contact with an end of the annular sealingmember and arranged opposing the opening end face of the socket at apredetermined distance from the opening end face of the socket, thepressing face being configured to press the annular sealing member; aplurality of protrusions arranged outside of the plurality of boltinsertion holes in the radial direction of the second passage formingmember to contact the opening end face of the socket and arrange thepressing face at the predetermined distance from the opening end face ofthe socket; and an escaping portion dimensioned to allow a part of theannular sealing member to escape when the part of the annular sealingmember is pressed by the pressing face, the escaping portion being arecessed portion dimensioned to create an opening near an area of theopening end face of the socket that is opposed to the escaping portion,the escaping portion being arranged inside of the plurality of boltinsertion holes in the radial direction of the second passage formingmember and outside of the pressing face in the radial direction of thesecond passage forming member, the escaping portion being recessed fromthe pressing face in a drawing direction of the spigot, wherein, in theradial direction of the second passage forming member, a clearancebetween the inner circumference of the socket and the outercircumference of the spigot is less than a distance between the outercircumference of the spigot and the escaping portion, wherein one of thefirst and second passage forming members is a valve and the other of thepassage forming members is a pipe, and wherein the pressing ring ismovable by the pressing member along the axis of the second passageforming member in the pressing direction so as to press the annularsealing member into the sealing member insertion space until theprotrusions contact the socket.
 16. The joint according to claim 15,wherein the valve includes a valve casing and a valve body that isconfigured to open and close a passage formed in the valve casing, andwherein the valve casing includes one of the socket and the spigot. 17.The joint according to claim 15, wherein the protrusions are arrangedadjacent to an outer circumference of the pressing ring.
 18. The jointaccording to claim 15, wherein the protrusions project in the pressingdirection.
 19. The joint according to claim 15, wherein positions atwhich the protrusions are arranged respectively correspond withpositions at which the plurality of bolt insertion holes is formed. 20.The joint according to claim 15, wherein the protrusions are arranged inline with the bolt insertion holes in the radial direction of the secondpassage forming member.
 21. The joint according to claim 15, wherein theperipheral wall of the inner periphery of the rear of the socketprotrudes inward from the inner circumference of the socket, wherein thesealing member insertion space is formed between the opening end face ofthe socket and the peripheral wall of the socket along a shared axis ofthe first and second passage forming members, wherein the end of theannular sealing member that is in contact with the pressing face is afront end of the annular sealing member, wherein the part of the annularsealing member that escapes into the escaping portion is the front endof the annular scaling member, wherein the pressing face is configuredto press the front end of the annular sealing member such that a rearend of the annular sealing member contacts the peripheral wall of thesocket before the plurality of protrusions contact the opening end faceof the socket, and wherein the rear end of the annular sealing memberthat is in contact with the peripheral wall of the socket is inhibitedby the peripheral wall of the socket from moving further into thesealing member insertion space.